Selecting a milling cutter

Selecting a milling cutter is not a simple task. There are many variables, opinions and lore to consider, but essentially the machinist is trying to choose a tool that will cut the material to the required specification for the least cost. The cost of the job is a combination of the price of the tool, the time taken by the milling machine, and the time taken by the machinist. Often, for jobs of a large number of parts, and days of machining time, the cost of the tool is lowest of the three costs.

• Material: High speed steel (HSS) cutters are the least-expensive and shortest-lived cutters. Cobalt-bearing high speed steels generally can be run 10% faster than regular high speed steel. Cemented carbide tools are more expensive than steel, but last longer, and can be run much faster, so prove more economical in the long run.^{[citation needed]} HSS tools are perfectly adequate for many applications. The progression from regular HSS to cobalt HSS to carbide could be viewed as very good, even better, and the best. Using high speed spindles may preclude use of HSS entirely.

• Diameter: Larger tools can remove material faster than small ones, therefore the largest possible cutter that will fit in the job is usually chosen. When milling an internal contour, or concave external contours, the diameter is limited by the size of internal curves. The radius of the cutter must be less than or equal to the radius of the smallest arc.

• Flutes: More flutes allows a higher feed rate, because there is less material removed per flute. But because the core diameter increases, there is less room for swarf, so a balance must be chosen.

• Coating: Coatings, such as titanium nitride, also increase initial cost but reduce wear and increase tool life. TiAlN coating reduces sticking of aluminium to the tool, reducing and sometimes eliminating need for lubrication.

• Helix angle: High helix angles are typically best for soft metals, and low helix angles for hard or tough metals.